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Simple inoculum standardizing system for antimicrobial disk susceptibility tests
Abstract:
A collaborative study was undertaken to evaluate a simple, convenient device which expedites inoculum standardization for antimicrobial disk susceptibility tests. The Inocupac system (Minnesota Mining & Manufacturing [3M] Co., St. Paul, Minn.) was used to perform disk tests in parallel with the standard Bauer-Kirby method. Five investigators tested 100 selected isolates, each in triplicate. Inter- and intralaboratory precision of both disk procedures was essentially comparable. The Inocupac system failed to consistently provide satisfactory growth with some streptococci, but when testing common gram-negative bacilli, staphylococci, and most enterococci, the Inocupac system gave zones about the same size (+/-2 mm) as the Bauer-Kirby procedure. Interpretive agreement between the two test systems varied from 90 to 99% with different antimicrobial agents, and repeated tests with the Bauer-Kirby method demonstrated the same degree of interpretive agreement. The Inocupac system is a valid alternative method for inoculating disk susceptibility tests.
Insights
The Inocupac system offers a convenient method for standardizing antimicrobial disk susceptibility tests, showing comparable precision to the Bauer-Kirby method for common bacteria. This system is a valid alternative for routine laboratory use.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Infectious Diseases
Background:
- Accurate inoculum standardization is crucial for reliable antimicrobial susceptibility testing.
- The Bauer-Kirby method is the standard but can be time-consuming.
- A need exists for efficient and convenient methods for inoculum standardization.
Purpose of the Study:
- To evaluate the Inocupac system as a device for expediting inoculum standardization in antimicrobial disk susceptibility testing.
- To compare the performance of the Inocupac system with the standard Bauer-Kirby method.
- To assess the inter- and intralaboratory precision and interpretive agreement of the Inocupac system.
Main Methods:
- A collaborative study involving five investigators.
- Testing of 100 selected bacterial isolates in triplicate using both the Inocupac system and the Bauer-Kirby method.
- Parallel performance evaluation of disk susceptibility tests.
Main Results:
- Inter- and intralaboratory precision of the Inocupac system was comparable to the Bauer-Kirby method.
- The Inocupac system showed limitations with some streptococci but performed well with gram-negative bacilli, staphylococci, and most enterococci.
- Zone sizes were similar (+/-2 mm) between the two methods for tested organisms.
- Interpretive agreement ranged from 90% to 99% across different antimicrobial agents.
Conclusions:
- The Inocupac system is a valid alternative method for inoculating disk susceptibility tests.
- The device expedites inoculum standardization, offering a convenient option for clinical laboratories.
- Further evaluation may be needed for specific challenging organisms like certain streptococci.